steelwork

Steelwork comprises the structural steel elements that form the primary frame of a building or bridge, typically fabricated from hot-rolled sections, plates, and hollow sections, then bolted or welded together on site. It carries vertical loads from floors, roofs and cladding down to the foundations, and resists horizontal forces from wind and seismic activity. The steelwork is usually completed before other trades begin work, making it the critical path item in most commercial and industrial construction programmes.

The main components are columns (vertical members), beams (horizontal spanning members), bracing (diagonal elements that resist lateral forces), and connections (bolted or welded joints). Common sections include Universal Beams (UBs), Universal Columns (UCs), and Hollow Structural Sections (HSS) in circular, rectangular or square profiles. The choice of section depends on span, load, and architectural constraints. Steel grades typically range from 250 MPa to 450 MPa yield strength, with S275 and S355 being the most common British grades.

Fabrication happens in a steel mill or specialist fabrication shop where sections are cut, drilled, and welded according to contract drawings. Members are then delivered to site, checked against the fixing drawings, and erected by trained crews using mobile cranes. Temporary propping supports the frame until sufficient connections are complete and concrete floors are cast and cured. Bolt holes are marked with layout lines, and bolts are tightened progressively from the centre outward to ensure even seating.

Common defects and constraints

Out-of-plumb columns, missing bolts, inadequate temporary propping, and corrosion from standing water or salt spray are frequent site issues. Steelwork tolerances are tighter than other trades, typically ±20 mm over 10 metres, so poor positioning disrupts cladding and partition installation downstream. Connection detail failures, inadequate welding quality, and bolt slippage under load have caused collapses in the past, so rigorous inspection during and after erection is mandatory.

The term steelwork distinguishes structural steel from reinforced concrete and masonry; it is also separate from lightweight framing (cold-formed sections) and steel cladding. In steel-frame buildings, the steelwork is usually unfinished and invisible in the final structure, concealed behind concrete, brick, plasterboard, or other materials. Fire protection, either by encasement or intumescent coating, is always required in buildings with occupancy.